In this letter, a method of reducing mutual coupling between the rectangular waveguide end-slot array and improving its gain is presented. In this antenna, the novel surface corrugated structure is symmetrically loaded at both sides of each slot element. Different from the suppression of surface wave in the choke grooves, the proposed corrugated structure would modulate surface wave propagation, resulting in the variation of surface energy strength distribution. The effectiveness of the proposed surface grooves is verified by numerical simulations and experimental testing. It is found that the mutual coupling level between two slot elements is observably decreased to be less than -40 dB after employment of surface grooves, and the gain of two slots array is also greatly enhanced by 4 dB. Furthermore, the influences of groove parameters on the mutual coupling level and radiation performance are discussed, respectively, and physical mechanism of this corrugated structure is investigated and compared to that of choke grooves as well.